If you or your staff drive vans for work, they need to be insured. Not only is this a legal requirement, your livelihood could be seriously threatened if your vehicle is out of action whereas insurance can offer you a replacement.
The law requires you to have third party only cover at the very least, which covers your liability for injury to others and damage to their property, but will not cover you for accidental damage to your own vehicle. If you intend to use your van for commercial use, by law you must have Hire and Reward insurance. This type can in fact be third party only, but it is normally just as expensive as it is higher risk insurance.
If you can't afford to shoulder repair costs in the event of an accident, your other options are third party fire and theft or a comprehensive policy, which will cover loss or damage to your own vehicle, personal effects and medical expenses.
A number of factors will determine your premium. Some insurers will offer a discount if the van is alarmed, all will conduct a risk assessment, taking into account your track record as a driver, your age, the vehicle's value and condition, what it's used for and typically has stored in it, its mileage and where it's kept.
As with all motor insurance, any withheld information regarding your history as a road user could potentially invalidate your claim if it comes to light.